Wednesday, July 1, 2015

Reactionless EM drive

Recently, a Chinese physicist claimed to have invented something that was previously only science fiction. I'm going to have to explain.
Most of our motion is thanks to Newton's 3rd law, which states that for every action, there is an equal but opposite reaction. In other words, to move forward, something else must be pushed backwards. When I walk, or drive, or take a train, my shoes or the vehicle are pushing the earth backward, to push me forward. The earth is pushed back a negligible amount.
This is bad news for rocketry, as there is now a tyranny of fuel requirements. In order for the rocket to move, it must eject fuel. The fuel has weight. More weight means less thrust for any particular expenditure of fuel. The rocket must be super powerful to move both itself, and the fuel required to move it, which requires still more fuel (because the additional fuel has mass, causing additional inertia).
So science fiction writers proposed the reactionless drive, in which no fuel is ejected. Instead, energy is inputted into the system, and somehow directly transferred into motion. This way any energy, such as solar power, nuclear power, or other systems that don't involve a constant stream of exhaust, could keep the rocket moving. The rocket would be much lighter, and thus easier to launch, maneuver, and power.
The EM drive is, if the reporting about it is correct, exactly that reactionless drive. Microwaves are bounced around in a container, imparting their energy in the desired direction of motion. Microwaves have essentially zero mass, and can be produced by electrical activity. Since electricity can be generated by all kinds of systems, any of these systems can power the rocket.
The drive as described now is not very efficient. Only 2% of the inputted energy becomes motion, the rest becomes heat, noise, and other wasted energy. This drive could not launch a rocket from the earth's surface, and would only really be useful for a rocket that is already in space. However, we can expect refinement of the device as time goes on.
And someday, in the distant future, a spacecraft will launch, unfurl its solar panels, and use a reactionless drive like the EM drive to speed it on its way to a distant star. A laser system in solar orbit is tracking the system and providing a steady steam of power. The craft accelerates, going faster and faster until it is traveling at a large percentage of the speed of light. After years of accelerating, it then reverses the process, slowing down until it arrives at a planet, orbiting the distant star. It then deploys its payload. Perhaps this is a scientific probe, to bring data of this distant world to scientists on earth. Perhaps this is a colony constructor, bringing a human colony to a distant world. Perhaps it is something that I can't even conceive of yet. But whatever it is, it will be glorious.

3 comments:

note that the inventor is British : Shawyer,but he proposed his device for e replication by Yang Juan.Fetta invented a variation, and it was tested by Nasa Eagleworks .some variation worked too...here is yang juan paperhttp://www.emdrive.com/yang-juan-paper-2012.pdfhere is a summaryhttps://www.reddit.com/r/Futurology/comments/34cq1b/the_facts_as_we_currently_know_them_about_the/NBF have many articleshttp://nextbigfuture.com/search/label/emdrive

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